To refute the claim of the pesticide manufacturers that the increase in the reported numbers of dead birds was solely due to more people looking for them, we need to find evidence that suggests there was a real increase in bird deaths caused by pesticide sprayings. Let's evaluate each option:
(A) The publicity given to bird deaths was largely regional and never reached national proportions.
- This option doesn't directly address whether there was an actual increase in bird deaths. It only talks about the regional extent of the publicity, which may or may not be related to the increase in reports.
(B) Pesticide sprayings were timed to coincide with various phases of the life cycles of the insects they destroyed.
- This option provides information about the timing of pesticide sprayings but doesn't directly refute the pesticide manufacturers' claim. It doesn't address whether the increase in bird deaths was due to more people looking or a real increase in deaths.
(C) No provision was made to ensure that a dead bird would not be reported by more than one observer.
- This option implies that there could be duplication in the reporting of dead birds, but it doesn't address whether there was a real increase in bird deaths. It focuses on reporting procedures.
(D) Initial increases in bird deaths had been noticed by agricultural workers long before any publicity had been given to the matter. - This option directly refutes the pesticide manufacturers' claim. If agricultural workers had noticed increases in bird deaths before any publicity, it suggests that the increase was not solely due to more people looking but rather a genuine increase in bird deaths associated with pesticide sprayings.
(E) Dead birds of the same species as those found in agricultural areas had been found along coastal areas where no farming took place.
- This option doesn't directly refute the pesticide manufacturers' claim because it discusses a different location (coastal areas) and doesn't address whether there was a real increase in bird deaths in agricultural areas.
Option (D) provides the most direct refutation of the pesticide manufacturers' claim, as it suggests that agricultural workers had observed increased bird deaths before any publicity about the issue. Therefore, (D) is the best choice to refute the claim.